As is generally known, a fuel cell system is a power generation system that directly converts chemical energy of a fuel to electrical energy.
The fuel cell system includes a fuel cell stack generating electrical energy. A fuel supply apparatus supplies fuel (hydrogen) to the fuel cell stack. An air supply apparatus supplies oxygen in the air to the fuel cell stack. A heat and water management apparatus disperses reaction heat of the fuel cell stack to the outside and controls the driving temperature of the fuel cell stack.
The fuel cell system generates electrical power by an electrochemical reaction and exhausts heat and water that are by-products of the electrochemical reaction.
FIG. 1 is an exploded perspective view illustrating a fuel cell stack according to the prior art. For convenience, one unit cell is shown in FIG. 1.
As shown in FIG. 1, the fuel cell stack applied to a fuel cell vehicle has a configuration in which unit cells are continuously disposed. The general fuel cell stack has a configuration in which a plurality of unit cells 20 are stacked between a pair of end plates 10.
Each unit cell 20 includes a membrane electrode assembly (MEA) 30, and two separating plates 40 disposed at respective sides of the MEA 30.
The MEA 30 includes a polymer electrolyte membrane to move protons, and a catalyst layer provided at respective sides of the polymer electrolyte membrane, so that hydrogen and oxygen can react, that is, an anode and a cathode at respective sides of the polymer electrolyte membrane.
A separating plate 40 with flow fields through which reaction hydrogen and oxygen are supplied to the anode and the cathode and water generated by the reaction is exhausted is disposed at the outside of the MEA.
One side of the separating plate 40 faces the cathode or the anode, the other side of the separating plate 40 faces the separating plate 40 of another unit cell 20. A fuel path is formed at one side of the separating plate 40 facing the anode, and an air path is formed at the other side of the separating plate 140 facing the cathode. A coolant path for circulating coolant is formed inside the separating plate 40.
A fuel inlet manifold 44 and a fuel manifold 45 communicating with the fuel path are formed at respective ends of the separating plate 40. An air inlet manifold 46 and an air outlet manifold 47 communicating with the air path are formed at respective ends of the separating plate 40. A coolant inlet manifold 48 and a coolant outlet manifold 49 communicating with the coolant path are formed at respective ends of the separating plate 40.
Moisture is generated in the cathode by an electrochemical reaction of the fuel cell stack, and some moisture generated from the cathode is diffused to the anode. When excessive moisture remains in a path supplying fuel gas, water is generated and a flooding phenomenon in which a large amount of condensed water remains occurs. When the air supplied to the fuel cell stack is blocked by water, performance and durability of the fuel cell is deteriorated, and power generating performance is decreased.
Hydrogen and oxygen are ionized by the chemical reaction of each catalyst layer, thus generating an oxidation reaction generating electrons at a hydrogen portion and a reduction reaction generating water at an oxygen portion.
It is known that the oxidization-reduction reaction occurring in the catalyst layer is most efficient within a range of 60-80 degrees Celsius. However, temperature of the air that flows through the air inflow manifold is relatively low, thus efficiency of the oxidization-reduction reaction is decreased.
That is, in order to improve efficient driving of the fuel cell stack, the temperature of the air that flows through the air inlet manifold 46 should be high, and an exhausted coolant through the separating plate 40 should be rapidly cooled.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.